1. Field of the Invention
The invention relates to an internal combustion engine in which power is generated by burning an air-fuel mixture in a combustion chamber, and a control method thereof. More particularly, the invention relates to an internal combustion engine and a control method thereof, which make it possible to activate a catalyst for purifying exhaust gas discharged from a combustion chamber early.
2. Description of the Related Art
Recently, it has become more and more important to reduce exhaust emissions such as HC, for example, immediately after an engine is started in a cold state, since enforcement of the emission control and the like is strengthened. Therefore, as disclosed in Japanese Patent Application Publication No. JP-A-8-296458, an in-cylinder injection internal combustion engine is known, in which a fuel injection valve injects fuel directly into a combustion chamber during an exhaust stroke so that unburned fuel (and air) is burned in a catalyst, whereby the catalyst is activated early. Also, as disclosed in Japanese Patent Application Publication No. JP-A-2001-304016, a technology is known, in which a fuel injection valve injects fuel during an expansion stroke, oxygen that becomes unnecessary during a compression stroke and CO that is generated due to incomplete combustion during the expansion stroke are supplied to a catalyst, and the catalyst is activated using heat of reaction between the oxygen and the CO when the engine is started in a cold state.
As disclosed in Japanese Patent Application Publication No. JP-A-2002-048035, an internal combustion engine with a turbocharger which makes it possible to improve fuel economy and suppress generation of smoke. The internal combustion engine with a turbocharger includes a port injector for injecting fuel into an intake port, and an in-cylinder injector for injecting fuel directly into a combustion chamber. Further, as disclosed in Japanese Patent Application Publication No. JP-A-4-183945, an in-cylinder injection internal combustion engine is known, in which a valve overlap period during which both of an intake valve and an exhaust valve are opened is increased during engine low-load operation so that the amount of high-temperature unburned gas that remains in a combustion chamber is increased, whereby the temperature of an air-fuel mixture is maintained at high temperature before ignition, evaporation of fuel is promoted, a combustion speed is improved, and combustion is stabilized.
However, as described above, even if the fuel is injected directly into the combustion chamber during the exhaust stroke or the compression stroke, it is difficult to reliably supply the catalyst with air of an amount necessary for activating (warming) the catalyst. Thus, the internal combustion engine needs to be further improved in order to reduce exhaust emissions, for example, immediately after the engine is started in the cold state.